It is known to provide a vehicle with a traction control system, which may be provided with various off-road modes, particularly but not exclusively 4×4 vehicles, and particularly but not exclusively for use in such vehicles that may be required to operate off-road and/or in challenging conditions, said conditions being challenging either as a result of terrain type or of weather conditions. Such conditions (and their associated modes) may include Grass, Gravel and Snow (GGS), but may also include rocky terrain (or ‘rock crawl’), mud and ruts, ice, sand and/or steep gradients. In particular, such vehicles may be required to make ascents on slopes comprising gradients that are particularly steep. Such vehicles may be provided with a ‘hill descent’ mode, which nominally means that a driver is not required to manually activate brakes or manually change gears in order to maintain a controlled descent of a steep slope. Hill descent methods are well known in the art and need not further be discussed here.
On occasion a vehicle may be driven up a slope on which ultimately it is unable to make further progress—a ‘failed ascent’. This may be as a result of insufficient power available to the vehicle from the engine or prime mover or, more usually, as a result of a loss of sufficient traction. It is not unknown for drivers of a vehicle in such a situation to feel a loss of control unless appropriately trained.
An appropriate response to a failed ascent in the prior art in a vehicle with a manual gearbox is a method as follows:
If the driver notices that the ascent of a slope has failed, i.e.: the wheels are driving but the vehicle is no longer ascending, or is even going backwards, the correct response is to brake hard and initiate an engine stall. In most circumstances the vehicle will then come to rest, braked, on the slope.
Alternatively, slope ascent may fail when the engine stalls. The correct response is also to brake in this scenario, so that the vehicle comes to rest, braked, on the slope.
In either case, the failed ascent results in the vehicle sitting at rest, braked, on the slope. Still pressing the brake pedal, the driver then opens the clutch (presses clutch pedal), selects reverse gear, and re-engages the clutch (releases clutch pedal).
The brake pedal is then released. The vehicle is then held on the slope by engine friction acting through the driveline and the engaged reverse gear.
The vehicle engine is then re-started. The vehicle then descends the slope in reverse gear under engine braking. If available, a hill descent mode may be used to assist in control of the descent, if one is available on the vehicle. Once the slope has been cleared, the driver of the vehicle may reattempt the ascent or choose an alternative route.
In a vehicle with an automatic gearbox, an equivalent method is as follows:
If the driver notices that the ascent has failed, the correct method of response is to brake so that the vehicle is at rest, braked, on the slope.
In some circumstances, an engine of the vehicle may stall in this scenario. The driver then brakes, selects neutral, restarts the engine, selects reverse and releases the brake. The vehicle will then descend the slope in a controlled fashion under engine braking in reverse gear.
Alternatively, if the vehicle has not stalled, the driver simply selects reverse and releases the brake—the vehicle will then descend the slope in a controlled fashion under engine braking in reverse gear.
Again, in either scenario (stall or non-stall), to assist in control of the descent, the driver may make use of the wheel brakes or, if available, a hill descent mode.
Once clear of the slope the ascent may be reattempted, or an alternative route may be chosen.
The Hill Ascent failure recovery methods noted above are known to skilled off-road driving practitioners. Inexperienced drivers, however, may panic upon the realisation that a hill ascent has failed. Where a failure is due to the limits of traction having been reached, for example, it is not an uncommon response to continue to attempt to drive up a slope by simply pressing harder on the accelerator. In a situation where the vehicle has stalled, a natural response is simply to brake hard. Further steps of selecting reverse and so on may not be known, and an attempt may be made to allow the vehicle to roll backwards down the slope with only the wheel brakes to control the descent. This is not advisable since, with no engine running, wheel brakes may not be as effective due to a lack of servo assistance, and a hill descent mode is also likely to be unavailable to assist in the descent.
Furthermore, vehicles tend to have a bias of braking to the front, so braking on descent in reverse tends to result in front wheel lock (unless a centre differential, where available, is locked), and an undesirable loss of lateral stability at the front end of the vehicle. Some drivers may attempt to re-start the vehicle and continue to attempt to drive up the gradient, leading to a very difficult hill-start and most likely to further failure.
What is required is an improved method of dealing with a failed hill ascent. The method may be one in which an appropriate response does not require driver input—in case the driver is inexperienced—and in which the maximum amount of control is retained.